Released
Datasheet
PM73487 QRT
PMC-Sierra, Inc.
PMC-980618
Issue 3
622 Mbps ATM Traffic Management Device
Product Overview
The PM73487 622 Mbps ATM Traffic Management Device (QRT ) is an advanced communica-
tions device capable of supporting very large, high-performance ATM switching systems. The
rich feature set of the QRT enables systems to offer many sophisticated network services. The
QRT provides 622 Mbps UTOPIA (Level 1 or Level 2) access to switch fabrics composed of
PM73488 5 Gbps ATM Switch Fabric Elements (QSEs). Together, these devices can be used to
build architectures with capacities from 622 Mbps to 160 Gbps. The QRT can also act as a stand-
alone 622 Mbps switch.
The QRT/QSE architecture virtually eliminates head-of-line blocking by means of the QRT’s per-
Virtual Channel (VC) receive queues and congestion feedback from the QSE switch fabric. The
distributed architecture acts as an output-buffered switch by incorporating Evil Twin Switching
(a congestion-reducing routing algorithm in the switch fabric) and a speed-up factor in the switch
fabric (running the fabric faster than the line rate).
The QRT uses per-VC receive queues, 64 receive Service Classes (SCs), and 16 transmit SCs per
each of the 31 Virtual Outputs (VOs) to enable flexible multi-priority scheduling algorithms. The
scheduler can be used to ensure Quality-of-Service (QoS) guarantees for Constant Bit Rate
(CBR), Variable Bit Rate (VBR), and Unspecified Bit Rate (UBR) VCs. The QRT also provides
five separate congestion thresholds, each with hysteresis, that selectively control AAL5 Early
Packet Discard (EPD) and/or Cell Loss Priority (CLP)-based cell dropping for UBR support.
Additional highlights of the QRT include full Virtual Path Indicator (VPI)/Virtual Channel Indi-
cator (VCI) header translation, separate input and output cell buffers (up to 64K each), Virtual
Path (VP)/VC switching, and support for up to 16K VCs on both the receive and transmit sides.
PMC-Sierra also offers the QRT Device Control Package, which is a software package that har-
nesses the QRT’s rich feature set and shortens system development times.
FEATURES
QUEUING ALGORITHMS
Receive
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Maintains 64 weighted, bandwidth-controlled SCs with per-VC queues.
Provides round-robin servicing of queues within each SC.
Provides per-channel (VP or VC), per-SC, and per-direction congested and maximum
queue depth limits.
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Provides up to 64K cell buffers.
Transmit
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Provides 31 VOs.
Maintains 16 SCs for each VO with per-VC accounting.
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PMC [ PMC-SIERRA, INC ]
